1. Field of the Invention
The invention relates to a radiation (e.g., ultraviolet radiation) fluid treatment systems and to a method for radiation (e.g., ultraviolet radiation) treatment of a fluid. More particularly, in a preferred embodiment, the invention relates to a treatment system which is controllable using both a kinetic model and a reactor model that interact with one another.
2. Description of the Prior Art
Ultraviolet fluid treatment systems are used, for example, in the disinfection or other treatment of fluids contaminated with microorganisms and in the oxidation and degradation of chemical contaminants. A variety of ultraviolet fluid treatment devices are used in these systems. See, for example, U.S. Pat. No. 4,872,980, U.S. Pat. No. Re 36,896, U.S. Pat. No. 6,500,346, International Publication Number WO 03/024,874 and International Publication Number WO 03/072,508, all of which are assigned to the assignee of the present invention. Each of these devices has a radiation zone in which the fluid is exposed to radiation (e.g., ultraviolet radiation) supplied by one or more radiation (e.g., ultraviolet) sources or lamps immersed in the fluid being treated.
There is an ongoing need to reduce or minimize the operating cost of radiation treatment systems such as ultraviolet fluid treatment systems. One of the operating costs is the electrical energy used to power the ultraviolet lamps. In some systems, especially those used in the oxidation of chemical contaminants, an oxidant, for example hydrogen peroxide and/or ozone, is added to the fluid prior to irradiation and is consumed during fluid treatment. The consumption of oxidant is another operating cost of these systems. Controlling the amount of electrical energy and, where applicable, the amount of oxidant used is important in reducing the overall operating costs of an ultraviolet fluid treatment system.
Various means of controlling ultraviolet fluid treatment systems have been proposed. Typically, these means do not use feedback control to optimize system operating parameters based on a comparison of fluid treatment system performance versus the treatment objectives. Usually, control is based only on a measurement of a single set of fluid properties, such as the transmittance of the fluid to ultraviolet light, the fluid flow rate, etc., and the measurement is typically made only upstream of the ultraviolet radiation zone. On rare occasions where feedback control has been used and measurements have been taken both upstream and downstream of the radiation zone, the time required for analysis of actual target contaminant concentration is typically too long to be practical for real-time control of the fluid treatment system operating parameters. In addition, a reactor model relating system operating cost to electrical energy consumption and, where applicable, oxidant consumption has not been previously employed for ultraviolet fluid treatment system control. Although kinetic models have been used to predict contaminant conversion, these models are based on measurements of the actual target contaminant concentration, not on more readily measured fluid properties that may be used to approximate system performance, and have not been linked with a reactor model to optimize system operating cost through control of system parameters.
U.S. Pat. No. 5,151,252 [Mass] discloses that the concentration of material in the fluid treatment chamber can be calculated from first order kinetics for photochemical reactions and that the fluid flow rate and/or lamp output may be adjusted as a function of concentration—see column 6, lines 2-20. No description is provided of a practical control system in which a kinetic model is used with a reactor model to control an ultraviolet fluid treatment system. Also, when using the Mass approach, the concentration of the contaminant must be measured. Measurement of contaminants typically cannot be completed rapidly enough to be useful in controlling the amount of electrical energy or oxidant supplied to the fluid treatment system on a real-time basis.
U.S. Pat. No. 6,023,065 [Garver, Jr.] discloses a method and apparatus for monitoring and controlling hydrogen peroxide and ozone concentrations in pulp and paper bleaching. The method and apparatus make use of ultraviolet light as a measurement tool for computing an empirical value of a characteristic of the effluent. The apparatus does not make use of ultraviolet light as part of a fluid treatment system and relies on a single empirical model for feedback control.
U.S. Pat. No. 6,269,680 [Prieve et al.] discloses a sterilization chamber using hydrogen peroxide in the vapour phase. Ultraviolet light is used as a measurement tool in assessing the concentration of hydrogen peroxide, which is used as a parameter in a feedback control system for a hydrogen peroxide dosing pump. Ultraviolet light is not used as part of a fluid treatment system and the controlled variable, hydrogen peroxide concentration, is measured directly, obviating the need for a kinetic model to determine the concentration.
The need therefore exists for improvements in the control of radiation fluid treatment systems such as ultraviolet fluid treatment systems.